Built-in reader mode

+1, but a massive one. At this time it's the only feature that bars me from making Opera my default browser. And if I'm not mistaken Mercury allows anyone to implement its parser, so no technical reason no to do it.

I tried the reading view in Microsoft Edge and was pleasantly surprised by it... There are some extensions for this but none of them work nicely, at least the few I tested. I tried to like Instapaper and while it's nice, I can't be bothered to go to a separate service to read stuff from the web. So, +1 on the built-in reader mode for Opera.